Messi and Ronaldo have dominated football for more than a decade, with the pair winning 11 Ballon d'Or awards between them as debate rages over who is the game's greatest player.
Ronaldo – Real Madrid's all-time leading goalscorer – has won five Champions League titles, three Premier League trophies, two Serie A crowns and as many LaLiga honors among other silverware throughout his career.
Messi likened five-time Ballon d'Or winner Ronaldo to Los Angeles Lakers superstar LeBron James.
"There are many admirable athletes. Rafa Nadal, Federer, LeBron - in all sports there is always someone who stands out and is admirable for his work," six-time Ballon d'Or winner and Barca's all-time leading scorer Messi told La Sexta.
"Cristiano stands out in football. There are many who stand out and always do their best."
Messi has won 33 trophies for Barca since debuting for the Spanish giants in 2004.
The 33-year-old – tipped to leave Camp Nou at the end of the season – has won four Champions League titles and 10 LaLiga trophies.
Messi set a new one-club goals record after netting for the 644th time, surpassing Pele's haul in a 3-0 LaLiga victory at Real Valladolid.
The Argentina skipper's 644 goals have come across 17 seasons and 749 games for Barca.
Messi's effort against Valencia on December 19 made him the first player to reach the 450 milestone for a single club in any of Europe's top five leagues.